1. Field of the Invention
The present invention relates to a transceiver and communication method of digital subscriber line, especially to a transceiver and communication method supporting a variety of digital subscriber line systems.
2. Description of Related Art
Digital subscriber line (DSL) system is a popular option for users to access internet, which uses the present telecommunication line to achieve the purpose of accessing broadband network. DSL system mainly includes an asymmetric digital subscriber line (ADSL) system and a very-high-data-rate digital subscriber line (VDSL) system, and the transceiver thereof adopts full-duplex transmission to allow users using a pair of telecommunication lines to transmit and receive signals at the same time, so as to fulfill the purpose of accessing broadband network. The hybrid circuit of said transceiver is a circuit design capable of satisfying full-duplex transmission in DSL system, which mainly uses a four-to-two circuit to transmit and receive signal simultaneously through a twisted pair, and thereby accomplishes effective transmission. In the view of customer premises equipment (CPE), the transmission (a.k.a. upstream) means the communication from a client end to a central office (CO) end while the reception (a.k.a. downstream) means the communication from a central office end to a client end.
Some prior arts about DSL system can be found in the US patents (U.S. Pat. Nos. 5,822,426; 6,163,579; 6,931,122; 7,072,464; 7,127,062; 7,170,927; 7,031,378; 7,106,854; 8,045,702) and US patent applications (publication number: 20110044415; 20090122845). However, the transceiver of these prior arts has at least one of the following problems: a single transceiver is not enough to support a variety of DSL systems, which makes applications inflexible and leads to higher cost; echo cancellation could not be carried out in light of transmission loop distance and DSL types, which leads to worse echo cancellation performance; echo noise escaping from the hybrid circuit could not be eliminated thereafter, which makes a reception end suffer the inter symbol interference (ISI) of said echo noise and leads to the reduction of signal-to-noise (SNR) ratio.
Therefore, the present DSL transceiver is not good enough, which means that this technical field needs a transceiver capable of supporting a variety of DSL systems and carrying out echo cancellation according to the transmission environment adaptively.